A rail adjustment system of this type, as is known from DE 198 15 283 C2 for example, comprises a drive motor which is fixed, centrally between two rails of a seat rail pair, to a mounting plate which is connected to the upper rails of said rails. Both sides of the drive motor are connected to a spindle nut which is mounted in a spindle gear mechanism by means of drive shafts which can also be designed as flexible shafts. Said spindle nut interacts with a threaded spindle which is arranged between an upper rail, which can be displaced in the longitudinal direction, and a lower rail which is stationary or fixed to the floor. A rotary movement of the drive motor is therefore converted into a longitudinal displacement of the respective upper rail in relation to the corresponding lower rail of the rail pair by means of the drive shafts and the spindle gear mechanism.
The flexible drive shaft, which has a rotating flexible core and a casing tube which is also flexible and surrounds said core, can be passed through an additional tube for the purpose of stabilizing its position. As an alternative, the flexible shaft can also be stabilized by support points for the rotating core being integrated in the flexible casing tube between the ends of said casing tube as per DE 102 00 985 B4.
While the provision of an additional support tube for the flexible drive shaft entails increased outlay on parts, a flexible drive shaft, whose flexible casing tube is provided with support points for the rotating core, is complicated in terms of production. In addition, rail adjustment systems whose spindle drives are equipped with drive shafts of this type have a tendency to create undesirable noise.